The recent trend in telecommunications has been the convergence of mobile communications and the Internet, resulting in various new technologies, new business models and business opportunities. One of the basic principles in introduction and development of new services has been interoperability. This means that notwithstanding of the communication technologies used for accessing the service, the user experience of the service should be more or less the same. One of the major obstacles in provision of such interoperable services are the different limitations of data throughput in different technologies. The new technologies have been designed from the beginning to support higher data rates, but the prevailing technologies offer often lower data rates. It is clear that the urge for new services happens much faster than the transition to the new technologies, and therefore it is essential that the data throughput of the existing technologies could be improved.
Spectrum space is probably the most limited and precious resource in the industrialized world, so mere addition of new channels to increase the throughput is not possible. The introduction of digital systems brought in a combination of frequency division multiplexing and time division multiplexing. In frequency division multiplexing a separate frequency band is allocated to each tributary channel in common channel. In time division multiplexing two or more lower bandwidth communications channels are combined into a higher bandwidth channel by allocating frequency time slots in turn to each of the lower bandwidth communications. By this manner the data rates over the air interface were significantly improved.
It soon became evident that the throughput of one timeslot was not adequate for new advanced services, and techniques for allocating channels for downlink and uplink in a multislot configuration and for grouping the channels into channel sets were introduced. The multislot configurations were first introduced to the circuit switched operation (High Speed Circuit Switched data, HSCSD) and adapted to the packet switched operation with the emergence of General Packet Radio System (GPRS).
The enhanced data rates for global evolution (EDGE) is an emerging solution to increase the throughput and capacity on the radio link of GSM. The improvement is implemented by introducing a new 8PSK (8 Phase Shift Keying) modulation technique. In the traditional GMSK (Gaussian Minimum Shift Keying) modulation of GMS one transmitted symbol represents one bit. In 8PSK modulation three consecutive bits are mapped onto one symbol, which means that in 8PSK the number of symbols delivered within a defined period of time remains the same as in GMSK, but the data rate is increased by a factor of three.
Both GPRS and EDGE support multi-slot connections, where one or more timeslots can be allocated for one connection. The theoretical maximum speeds of EDGE thus range up to 473 kilobits per second (kbps), but such rates would require a single user taking over all eight timeslots, and coding would be implemented without any error protection. Such connections are not practical and thus very unlikely. Current measured EDGE rates are approximately 60 kbps at cell borders, and approximately 150 kbps on an average, achieved with an asymmetric connection of five downlink slots and one uplink slot. However, as discussed above, for modern real-time applications, higher data rates would be required. Due to the asymmetric nature of Internet usage, increasing the data rates especially in the downlink side would be important